fix(codemod): preserve source pin when migrating tools.serena

pkg/cli/codemod_serena_import.go

@@ -14,12 +14,12 @@ var serenaImportCodemodLog = logger.New("cli:codemod_serena_import")
 
 // getSerenaToSharedImportCodemod creates a codemod that migrates removed tools.serena
 // or engine.tools.serena configuration to an equivalent imports entry using
-// shared/mcp/serena.md, and may normalize a pinned source ref to @main.
+// shared/mcp/serena.md. The existing source: pin is preserved unchanged.
 func getSerenaToSharedImportCodemod() Codemod {
 	return Codemod{
 		ID:           "serena-tools-to-shared-import",
 		Name:         "Migrate tools.serena or engine.tools.serena to shared Serena import",
-		Description:  "Removes 'tools.serena' or 'engine.tools.serena', adds an equivalent 'imports' entry using shared/mcp/serena.md with languages, and may rewrite a pinned 'source:' ref to '@main'.",
+		Description:  "Removes 'tools.serena' or 'engine.tools.serena' and adds an equivalent 'imports' entry using shared/mcp/serena.md with languages. The existing 'source:' pin is preserved.",
 		IntroducedIn: "1.0.0",
 		Apply: func(content string, frontmatter map[string]any) (string, bool, error) {
 			languages, ok := findSerenaLanguagesForMigration(frontmatter)
@@ -45,7 +45,6 @@ func getSerenaToSharedImportCodemod() Codemod {
 				return addSerenaImport(result, languages), true
 			})
 			if applied {
-				newContent = maybeUpdatePinnedSourceRef(newContent, frontmatter)
 				if alreadyImported {
 					serenaImportCodemodLog.Print("Removed tools.serena (shared/mcp/serena.md import already present)")
 				} else {
@@ -324,31 +323,3 @@ func hasNestedContent(lines []string, startIndex int, blockIndent string) (bool,
 
 	return false, len(lines)
 }
-
-func maybeUpdatePinnedSourceRef(content string, frontmatter map[string]any) string {
-	sourceAny, hasSource := frontmatter["source"]
-	if !hasSource {
-		return content
-	}
-
-	source, ok := sourceAny.(string)
-	if !ok || strings.TrimSpace(source) == "" {
-		return content
-	}
-
-	sourceSpec, err := parseSourceSpec(source)
-	if err != nil {
-		return content
-	}
-
-	if sourceSpec.Repo != "github/gh-aw" || !IsCommitSHA(sourceSpec.Ref) {
-		return content
-	}
-
-	updatedSource := sourceSpec.Repo + "/" + sourceSpec.Path + "@main"
-	updatedContent, err := UpdateFieldInFrontmatter(content, "source", updatedSource)
-	if err != nil {
-		return content
-	}
-	return updatedContent
-}

pkg/cli/codemod_serena_import_test.go

@@ -196,7 +196,7 @@ engine:
 		assert.False(t, hasEngineTools, "Engine tools should be removed after migration")
 	})
 
-	t.Run("updates github/gh-aw source pin from commit SHA to main when migrating serena", func(t *testing.T) {
+	t.Run("preserves github/gh-aw source pin when migrating serena (does not rewrite to @main)", func(t *testing.T) {
 		content := `---
 source: github/gh-aw/.github/workflows/duplicate-code-detector.md@852cb06ad52958b402ed982b69957ffc57ca0619
 engine: copilot
@@ -217,10 +217,66 @@ tools:
 		result, applied, err := codemod.Apply(content, frontmatter)
 		require.NoError(t, err, "Codemod should not return an error")
 		assert.True(t, applied, "Codemod should be applied when tools.serena is present")
-		assert.Contains(t, result, "source: github/gh-aw/.github/workflows/duplicate-code-detector.md@main", "Codemod should update pinned gh-aw source to main")
+		assert.Contains(t, result, "source: github/gh-aw/.github/workflows/duplicate-code-detector.md@852cb06ad52958b402ed982b69957ffc57ca0619", "Codemod should preserve the original pinned commit SHA in source")
+		assert.NotContains(t, result, "@main", "Codemod should not rewrite source pin to @main")
 		assert.Contains(t, result, "- uses: shared/mcp/serena.md", "Codemod should still add shared Serena import")
 	})
 
+	t.Run("storybookjs and FluidFramework: preserves pinned source and migrates tools.serena to imports", func(t *testing.T) {
+		// Simulates the duplicate-code-detector.md workflow used by storybookjs/storybook and
+		// microsoft/FluidFramework, both sourced from gh-aw at the same pinned commit.
+		// The codemod must migrate tools.serena without touching the source pin.
+		tests := []struct {
+			name string
+		}{
+			{name: "storybookjs/storybook"},
+			{name: "microsoft/FluidFramework"},
+		}
+
+		content := `---
+source: github/gh-aw/.github/workflows/duplicate-code-detector.md@852cb06ad52958b402ed982b69957ffc57ca0619
+name: Duplicate Code Detector
+description: Identifies duplicate code patterns across the codebase
+on:
+  workflow_dispatch:
+  schedule: daily
+permissions:
+  contents: read
+  issues: read
+  pull-requests: read
+engine: copilot
+tools:
+  serena: ["typescript"]
+imports:
+  - shared/mood.md
+strict: true
+---
+
+# Duplicate Code Detection
+`
+		frontmatter := map[string]any{
+			"source": "github/gh-aw/.github/workflows/duplicate-code-detector.md@852cb06ad52958b402ed982b69957ffc57ca0619",
+			"engine": "copilot",
+			"tools": map[string]any{
+				"serena": []any{"typescript"},
+			},
+			"imports": []any{"shared/mood.md"},
+		}
+
+		for _, tt := range tests {
+			t.Run(tt.name, func(t *testing.T) {
+				result, applied, err := codemod.Apply(content, frontmatter)
+				require.NoError(t, err, "Codemod should not return an error")
+				assert.True(t, applied, "Codemod should be applied when tools.serena is present")
+				assert.Contains(t, result, "source: github/gh-aw/.github/workflows/duplicate-code-detector.md@852cb06ad52958b402ed982b69957ffc57ca0619", "Source pin must be preserved unchanged")
+				assert.NotContains(t, result, "@main", "Source pin must not be rewritten to @main")
+				assert.Contains(t, result, "- uses: shared/mcp/serena.md", "Serena import must be added")
+				assert.Contains(t, result, `languages: ["typescript"]`, "Serena import must include languages")
+				assert.NotContains(t, result, "  serena:", "tools.serena must be removed")
+			})
+		}
+	})
+
 	t.Run("falls back to engine.tools.serena when top-level tools.serena is invalid", func(t *testing.T) {
 		content := `---
 engine: